• Determine population pharmacokinetics for children with systemically active SOJRA at 0.4 mg/kg etanercept twice weekly and at 0.8 mg/kg twice weekly [ Time Frame: 13 months ] [ Designated as safety issue: No ]
• Determine the effect on the cytokine profile in a substudy [ Time Frame: 13 months ] [ Designated as safety issue: No ]
• Determine the time to response during open-label treatment with etanercept [ Time Frame: 13 months ] [ Designated as safety issue: No ]
• Determine the safety of etanercept in pediatric subjects with systemically active SOJRA [ Time Frame: 13 months ] [ Designated as safety issue: No ]
• Determine the mean time to flare (up to 3 months) following withdrawal of etanercept in Part-2 [ Time Frame: 13 months ] [ Designated as safety issue: No ]
• Determine the safety and benefit of higher doses of etanercept (up to 0.8 mg/kg twice weekly) in Part-1B for children who have had a partial response to etanercept at 0.4 mg/kg twice weekly in Part-1A [ Time Frame: 13 months ] [ Designated as safety issue: No ]

• Determine the time to response during open-label treatment with etanercept
• Determine the safety of etanercept in pediatric subjects with systemically active SOJRA
• Determine the mean time to flare (up to 3 months) following withdrawal of etanercept in Part-2
• Determine the safety and benefit of higher doses of etanercept (up to 0.8 mg/kg twice weekly) in Part-1B for children who have had a partial response to etanercept at 0.4 mg/kg twice weekly in Part-1A
• Determine population pharmacokinetics for children with systemically active SOJRA at 0.4 mg/kg etanercept twice weekly and at 0.8 mg/kg twice weekly
• Determine the effect on the cytokine profile in a substudy

Rationale: etanercept inhibits the effects of tumor necrosis factor, which plays an important role in the progression of rheumatoid arthritis. A study of children with polyarticular course juvenile rheumatoid arthritis showed that Enbrel had efficacy and was generally well tolerated in children ages 4-17 who had moderately to severely active disease and who failed treatment with one or more disease modifying antiarthritic drugs. The children in the study may have had arthritis onset of pauciarticular, polyarticular, or systemic nature. Systemic onset juvenile rheumatoid arthritis (SOJRA) may result in approximately one-third of patients having significant long-term disability. Purpose: the Phase 4 study is designed to further define the safety and efficacy of etanercept in those children with SOJRA.

• Drug: Enbrel
• Drug: Placebo

INCLUSION CRITERIA:

• 2 - 18 years of age
• SOJRA for at least 3 months, with stable systemic features
• If taking methotrexate, hydroxychloroquine, or NSAIDs, dose must be stable
• Must take prednisone at a stable dose EXCLUSION CRITERIA:
• Need for other DMARDs or prestudy requirements for oral or parenteral pulse steroids or intra-articular steroids
• Pregnant or nursing female
• Clinically significant abnormal laboratory test results for blood cells, liver or kidney function, or serology
• Previous receipt of any TNF inhibitor
• Live virus vaccine within 12 weeks of study entry
• Participation in another study requiring informed consent within 12 weeks of entry
• Diabetes that requires insulin treatment
• Infection, chronic, recurrent, or currently active
• Any serious medical or psychiatric condition or history of alcohol or drug abuse